flutter - Flutter/Dart组按日期列出

Question

我有以下 map 列表，

[
   {
      "FullName":"Harry Potter",
      "DateOfBirth": "2020/02/16",
      "Department":"Branch Operation",
      "BirthDay":"Friday"
   },
   {
      "FullName":"John Wick",
      "DateOfBirth": "2020/02/16",
      "Department":"Finance",
      "BirthDay":"Friday"
   },
   {
      "FullName":"Solomon Kane",
      "DateOfBirth":2020/02/19,
      "Department":"Loan",
      "BirthDay":"Monday"
   }
]

我想操纵上面的数据，以使数据按其 DateOfBirth分组，以便结果看起来像这样。

[
   {
      "DateOfBirth": "2020/02/16",
      "BirthDay": "Friday",
      "Data":[
         {
            "FullName": "Harry Potter",
            "Department":"Branch Operation",
         },
         {
            "FullName":"John Wick",
            "Department":"Finance",
         }
      ]
   },
   {
      "DateOfBirth": "2020/02/19",
      "BirthDay": "Monday",
      "Data":[
         {
            "FullName":"Solomon Kane",
            "Department":"Loan"
         }
      ]
   },
]

在Javascript中，可以通过使用 reduce函数然后使用对象键映射来实现。
我也知道dart具有有用的软件包 collection

由于我不熟悉 Dart 和 Dart ，所以我不确定该怎么做。有人可以帮我吗？

谢谢

Answer 1

您可以使用fold并执行类似的操作

const data = [...];

void main() {
 final value = data.fold(Map<String, List<dynamic>>(), (Map<String, List<dynamic>> a, b) {
   a.putIfAbsent(b['DateOfBirth'], () => []).add(b);
   return a;
 }).values
   .where((l) => l.isNotEmpty)
   .map((l) => {
     'DateOfBirth': l.first['DateOfBirth'],
     'BirthDay': l.first['BirthDay'],
     'Data': l.map((e) => {
       'Department': e['Department'],
       'FullName': e['FullName'],
     }).toList()
 }).toList();
}

还是这样，如果您想使用传播运算符，我不知道它是否可读性强。

 final result = data.fold({}, (a, b) => {
     ...a,
     b['DateOfBirth']: [b, ...?a[b['DateOfBirth']]],
 }).values
   .where((l) => l.isNotEmpty)
   .map((l) => {
     'DateOfBirth': l.first['DateOfBirth'],
     'BirthDay': l.first['BirthDay'],
     'Data': l.map((e) => {
       'Department': e['Department'],
       'FullName': e['FullName'],
     }).toList()
 }).toList();